1. Field
Embodiments of the present invention relate generally to an alignment mark, a method of aligning a substrate including such an alignment mark, a substrate including such an alignment mark, a device manufacturing method and a device manufactured accordingly.
2. Background
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to transfer the pattern onto the target portion with high accuracy, the position of the target portion needs to be measured before transfer. To do this, the substrate may include alignment marks, for instance formed in scribe lanes in between target portions, of which the position can be measured using alignment sensors. The alignments marks may also be referred to as scribe lane marks. The alignment marks may thus be used to position the substrate with respect to for instance a projection system and the patterning device.
Usually, different types of alignment marks are provided. A first alignment mark may be provided for determining a position in a first direction (e.g. x-direction) and a second alignment mark may be provided for determining a position in a second direction (e.g. y-direction). In practice, usually a number of first and second alignment marks are provided for accurate position determination.
Scribe lane marks may be used because they can be exposed in the scribe lane together with the product image alongside a neighboring product image. These scribe lane marks can be used for one alignment direction (X or Y). Detection of two separate marks at a different moment and location is cause for small metrology errors. Furthermore the area occupied for alignment is perceived as too large and the time required to align segments in two directions is too long.
Intrafield alignment (for intrafield exposure correction) is only possible in the direction of the scribe lane and is therefore missing one direction. Only at the cost of cross-talk or for using wide scribe lanes can the alignment information in the direction perpendicular to the scribe lane be obtained.
In general there is a need for better reproduction of alignment to allow better overlay for double patterning and exposure.
Accordingly, a number of problems are identified according to the state of the art:                System overlay would benefit from better reproduction;        Alignment mark area is relatively large;        Current scribe lane marks have separate X and Y alignment positions, which can cause small overlay errors;        Current detection of a mark in a specific orientation (X or Y) is corresponding to movement of the stage along the axis causing most interferometer noise (air flow) instead of determining the position in the non-scanning direction, which may result in a bit lower noise level; and        Currently intrafield alignments in the direction perpendicular to the scribe lane can not properly be performed and alignment of X and Y positions in the same scribe lane is not possible in a practical way.        